Toothed belts have been widely used for power transmission in internal combustion engines of automobiles, and the like. Recently, toothed belts have been increasingly used in high-temperature and high-load environments. That is, downsizing of engines or the like requires toothed belts to be used in environments with higher temperature and to be smaller in width. Conventionally, to enhance the durability of a toothed belt in a high-load environment, for example, a short fiber or the like is incorporated into the tooth rubber, and rubber with a relatively high modulus based on a so-called performing technology is used as the tooth rubber.
Furthermore, in a high-temperature environment the amount of deformation sustained by the teeth of a toothed belt increases. Hence, the amount of internal heat generation is increased, and consequently the toothed belt is more likely to thermally degrade. In addition, the rubber and the fabric at tooth root portions are repeatedly elongated to a great extent, and consequently cracks are more likely to occur in the toothed belt. Conventionally, the fabric, the short fiber, the cord, and the like are subjected to surface treatment with RFL, rubber cement, or the like for prevention of cracks and the like, so that the adhesive forces of rubber with these members are enhanced.
Moreover, as disclosed, for example, in Patent Document 1, a V-ribbed belt is known which has such a structure that a resorcin-formalin resin or a melamine resin is incorporated into an adhesion rubber to enhance the adhesive force between the cord and the adhesion rubber in which the cord is embedded.    Patent Document 1: Japanese Patent Application Publication No. 2008-261489